1. Field of the Invention
The present invention relates to an image display medium which can be reiteratively writable, and particles for a display device used therefor, and an image forming device.
2. Description of the Related Art
Conventionally, display techniques such as Twisting Ball Display (display by rotation of particles separately colored with two-colors), electrophoresis, magnetophoresis, thermal rewritable medium, liquid crystals having memory ability, and the like have been provided as a reiteratively writable image display medium. These display techniques provide good memory ability of images, but they have problems that the display surface is not displayed as white as paper and that the contrast is decreased.
As a display technique using a toner, which solves the above-mentioned problems, Japan Hardcopy '99, collected papers, pp. 249-252 suggests a display technique, which displays an image by enclosing a electro-conductive color toner and white particles between opposed electrode substrates, injecting electric charge to the electro-conductive color toner via a charge transport layer provided on the surfaces inside of the electrodes of the non-displaying substrate, wherein the charge-injected electro-conductive color toner moves to the display substrate positioned opposed to the non-displaying substrate via the electric field between the electrode substrates, and the charge-injected electro-conductive color toner adheres inside of the display substrate to display an image by the contrast of the electro-conductive color toner and white particles.
The display technique is superior in that the image display medium is entirely composed of solid, and that the display by black and white can be converted by 100% in principle. However, according to the technique, there exist electro-conductive color toner being not contacted with the charge transport layer provided on the surface of inside of the electrode of the non-displaying substrate and electro-conductive color toner isolated from the other electro-conductive color toner. Since these electro-conductive color toners are not injected with electron charge, they exist randomly in the gap between the substrates without moving by electric field, which causes problem of decrease in contrast.
In order to improve such problems, an image display medium comprising a pair of substrates and plural kinds of particles, which are enclosed between the substrates, wherein the particles can move between the substrates by applied electron charge and having different colors and electrification properties, has been provided. According to the providing, high whiteness and high contrast can be obtained.
According to the providing, high whiteness and high contrast can be obtained. The composition of the provided particles is superior in initial density of whiteness, initial density of blackness and initial contrast. However, when the medium is reiteratively written, the contrast is decreased due to decrease in the density of the image, and image unevenness is generated due to decrease in the uniformity of the image.